Interface Converter

All Superinterfaces:
Cloneable, RelNode, RelOptNode
All Known Implementing Classes:
AbstractConverter, CassandraToEnumerableConverter, ConverterImpl, ElasticsearchToEnumerableConverter, EnumerableBindable, EnumerableInterpretable, EnumerableToSparkConverter, GeodeToEnumerableConverter, InnodbToEnumerableConverter, InterpretableConverter, JdbcToEnumerableConverter, JdbcToSparkConverter, MongoToEnumerableConverter, NoneConverter, PigToEnumerableConverter, SparkToEnumerableConverter

public interface Converter extends RelNode
A relational expression implements the interface Converter to indicate that it converts a physical attribute, or trait, of a relational expression from one value to another.

Sometimes this conversion is expensive; for example, to convert a non-distinct to a distinct object stream, we have to clone every object in the input.

A converter does not change the logical expression being evaluated; after conversion, the number of rows and the values of those rows will still be the same. By declaring itself to be a converter, a relational expression is telling the planner about this equivalence, and the planner groups expressions which are logically equivalent but have different physical traits into groups called RelSets.

In principle one could devise converters which change multiple traits simultaneously (say change the sort-order and the physical location of a relational expression). In which case, the method getInputTraits() would return a RelTraitSet. But for simplicity, this class only allows one trait to be converted at a time; all other traits are assumed to be preserved.

  • Method Details

    • getInputTraits

      RelTraitSet getInputTraits()
      Returns the trait of the input relational expression.
      input trait
    • getTraitDef

      @Nullable RelTraitDef getTraitDef()
      Returns the definition of trait which this converter works on.

      The input relational expression (matched by the rule) must possess this trait and have the value given by getInputTraits(), and the traits of the output of this converter given by RelOptNode.getTraitSet() will have one trait altered and the other orthogonal traits will be the same.

      trait which this converter modifies
    • getInput

      RelNode getInput()
      Returns the sole input relational expression.
      child relational expression